says dr. tim ferris of partners, account for the biggest portion of all costs. >> about 50% of the total is accounted for by 5% of the patients. they're so complicated that, left to their own devices, they will bounce between providers, and that movement between providers, uncoordinated, leads to waste in the system. >> reporter: so, partners assigns care managers to coordinate the treatment of high-risk cases. the elderly, for example, fall so frequently that, in 2010, over two million were treated in the e.r. >> and emergency room doctors really don't have a lot of choices; they're going to admit that patient. but when someone who knows the patient shows up in the emergency room and says, "actually, i know this person; it's okay; she'll be safe going home; i'm going to follow up closely with her," that changes the equation.